In recent years, it is required to reduce particulate matter (Particulate Matter: PM) discharged with exhaust gas from an internal-combustion engine, and the legal control is strengthened. Therefore, in case of a diesel engine, it is common to remove particulate matter by preparing a filter in the course of exhaust gas. The filter collects and removes the particulate matter from the exhaust gas passing through the filter. Such a removal of the particulate matter using a filter is investigated also for a gasoline engine.
If the collected particulate matters are accumulated too much, exhaust gas cannot pass through the filter. As a result, the fuel consumption of the internal-combustion engine is increased. For this reason, it is necessary to remove the particulate matter accumulated on the filter by burning, before the collected particulate matters are accumulated too much, as a reproduction process for recovering the function.
Moreover, in the reproduction process, if an abnormality such as melting or crack arises, since the temperature of the filter is raised too much, the particulate matter cannot appropriately be collected. Therefore, it is desirable to detect the abnormality in the filter, in addition to the reproduction process.
Patent Literature 1 describes a system including a pressure difference sensor to presume the quantity of particulate matters deposited on a filter and to perform an abnormality determination of the filter. In detail, the system detects an abnormality in the filter based on a variation in the pressure difference between an upstream side and a downstream side of the filter (hereafter this is also called as “a pressure difference of a filter”). An offset error may be generated in the pressure difference sensor. In Patent Literature 1, the influence of the offset error is eliminated by performing the abnormality determination of the filter based on the variation in the pressure difference of the filter, such that the detection accuracy is raised.